Dry drilling of diamonds and the like



Patented Dec. 23, 1952 UNITED STATES PATENT OFFICE DRY DRILLING OF DIAMONDS AND THE LIKE Chauncey G. Peters, Calvert County, Md., and Forest K. Harris, Washington, D. 0., assignors to the United States of America as represented by the Secretary of Commerce (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 4 Claims.

The invention herein described may be made and used by or for the Government of the United States Without payment to us of any royalty therefor.

The invention of our application Ser. No. 718,093 now Patent No. 2,552,582, of which the present application is a division relates to the drilling of diamonds and the like, and is particularly applicable in the production of wire drawing dies of such hard, crystalline material. The invention claimed in the said application (now Patent No. 2,552,582, issued May 15, 1951) is based on our discovery that diamonds and the like may be started and pilot drilled for the formation of the bell cones therein with greatly increased speed and with other marked advantages by impressing across a drill needle and stone condensed current and potential surges of short time duration applied to a non-rotated drill point in air or other gaseous environment with the energy of such surges controlled to maintain an energy input sufficient to produce disintegration at the point of contact by ionic bombardment but not so high as to cause a rise of temperature of the diamond that would initiate massive destruction thereof by oxidation, cause the rapid formation of a slender pilot hole or well in the diamond surface aligned with and entered by the needle point. The said invention resides in the provision of a method of and apparatus for making practical application of this discovery in the drilling of diamonds.

The present invention is in part disclosed as a sub-combination in our copending joint application with Walter B. Emerson, Irving L. Cooter, and Karl F. Nefilen, now Patent No. 2,438,941 issued April 6, 1948, wherein the present invention is employed in drilling the bell in the production of diamond dies. The present invention is likewise in part disclosed in the article published within one year prior to the application of which this application is a division in The American Minerologist 31:156-160, and entitled Application of the High Voltage Are to the Cutting, Sawing, and-Drilling of Diamonds by Chauncey G. Peters, one of the present applicants.

As the invention is well exemplified by the use thereof in the drilling of the hell or primary cone of a diamond die of definite size, such application is herein described as illustrative but not restrictive of the invention.

(A) Die production in general 'In general, the production of diamond dies involves the following steps: (1) selection and preparation of die blanks, (2) spotting, or starting the hole, (3) drilling the bell or primary cone, (4) drilling the secondary cone, (5) back-opening, and (6) polishing of the die surface. The present invention is particularly applicable in steps (3) and (4) of this procedure.

(B) Prior art practice (1) (2) In accordance with the prior art, for dies of .0015 inch diameter, or less, diamonds of /6 to 2; carat, allowing a thickness or" 1.3 to 1.8 millimeters, have been selected. The selected diamond has then been formed into a fiat plate having two parallel surfaces spaced apart by the thickness of the die, this being generally accomplished by bruting. This blank has then been mounted and centered in a metal disc which is rotated in a bench lathe while a small conical hole is spotted or bruted in one of the flat surfaces of the stone with a diamond chip held in a pair of pliers, to act as a starting point for the drill. The blank is then ready for the drilling operation.

(3) The method and equipment developed in Europe for drilling diamond dies (see Paul Grodzinski, Diamond and Gem Stone Industrial Production, Chap. II, page 169) essentially employ a star-drilling action. The drilling machine has a horizontal, single spindle that rotates at about 3500 revolutions per minute and carries a sewing needle for the drill. The diamond is mounted on a second spindle which oscillates the diamond against the sharpened end of the drill. Diamond dust of different grades mixed with alcohol or oil is used as the abrasive. Domestic machines as heretofore employed have operated on the same principle but usually employ ten vertical spindles to conserve space and facilitate inspection by the operator.

For drilling the primary cone, in the prior art the spotted blank is placed on the rough drilling machine, using a needle of about .040 inch diameter ground to a rather blunt point. Diamond dust of about 60 micron grade (our designation for dust having an average particle size of from to 70 microns) is used for the first part of the operation, and of about 30 micron grade (25 to 35 microns) for the finish. In this way the bell is formed, preferably as a cone of about 1 millimeter or .040 inch depth.

The time required to complete the spotting of a die by the old bruting method usually amounts to about hour, and the time for drilling the primary cone by the old method averages from 10 hours to 25 hours.

3 (C) Objects of this invention The invention of this divisional application has for its objects, severally and interdependently, the production of an improved work holder or window-nib for use in diamond drilling, including a cup with viewing apertures and a diamond holding plug adapted to be inserted in such cup so that the diamond is visible through the apertures during such drilling, and the provision of an improved method of drilling and/ or countersinking a small diamond die with the aid thereof. Further objects and advantages of the invention will be apparent from the detailed description of the illustrative embodiment of method and means incorporating its principles.

(D) The general procedure Briefly, in applying the invention of our application Ser. No. 718,093, now Patent No. 2,552,582, in the production of small diamond dies, following preparation of the blank by any suitable method, for example, that of the copending application above mentioned, we spot drill a pilot hole in the diamond surface by a dry drilling method, shape it to the form of a wide angle, say 90, cone preferably by a countersinking method employing a blunt countersinking needle and, eliminating the star drilling principle, extend a second pilot hole from the bottom of the wide angle cone by an electrical dry drilling method, and shape the resulting funnelshaped hole into a final primary cone which may be a 40 to 70 cone, for example, preferably by a countersinking method. The invention of the present application is particularly concerned with the work holding means for facilitating the countersinking method and with the steps performed in conjunction therewith.

In the accompanying drawings of embodiments illustrative of the several features of this invention:

Fig. 1 is a flow diagram of the steps of forming a primary cone by the dry drilling and countersinking method of our aforesaid parent application.

Fig. 2 is a comparative diagram of the conventional prior art process.

Fig. 3a is a diagram of the dry drilling method and means of said parent application.

Fig. 3b is a perspective view of one embodiment of dry drilling stand.

Fig. 4 is a diagram of countersinking apparatus partly in section illustrative of the present invention.

Referring to Figs. 1 and 2 of the accompanying drawings, Fig. 1 illustrates diagrammatically operations performed on the blank by the method of our parent application, and Fig. 2 shows in similar diagram for reference and comparison the steps employed in the prior art. In these figures, for ease of reference the several procedural steps are numbered and described with legends showing the approximate time to perform them.

As indicated in Fig. 1, by the procedure of our application Ser. No. 718,093, now Patent No. 2,552,582, after the die blank has been prepared, as by cutting and polishing its facial surfaces, a pilot hole is foredrilled into the diamond by means of an electric spark, and the operation is completed by a light commercial drilling machine modified to effect countersinking. In the latter operation the rotating drill follows the pilot hole without being deterred by apexial contact with the diamond, and the conical surface 4 of the drill, which is rotated with considerable peripheral speed, acts as a countersink or reamer for shaping the contours of the cones and applying the polish to the cone and bearing surfaces. Thus the tedious and time consuming star drilling operation, which is the basis of prior methods, is eliminated, and the strains, flaws, and fractures, and other damage to the bearing surfaces frequently resulting from preparing the blank and spotting the die by bruting, is avoided.

(1) Preparing the blank In the production of small diamond dies of the type disclosed in the above mentioned copending application, as the first step the blank is preferably prepared with two polished parallel surfaces and a polished window face at right angles thereto. Any desired method may be employed for preparing the blank, that disclosed in the above mentioned Patent No. 2,438,941 being preferred.

For forming the bell, the blank prepared in any suitable manner by step (1) is subjected to further steps as follows: (2) the blank is pilot drilled electrically; (3) the hole is then enlarged by mechanical countersinking; (4) the pilot hole is then extended; and (5) the bell shape may then be completed by mechanical countersinking, all as illustrated diagrammatically in Fig. 1. As there indicated, this complete operation when employing the present invention may be performed in from to minutes as compared with 10 to 25 hours by the old bruting and pecking method (Fig. 2, diagrams 2 and 3). Each of these steps will now be considered in detail.

(2) Foredrilling the pilot hole For forming the pilot hole, step (2), Fig. 1, apparatus is preferably used corresponding to that illustrated in Figs. 3a and 31). As shown in Fig. 3a, the leads from the volt, 60 cycle A. C. outlet are connected to the primary terminals of a zero to volt output adjustable ratio autotransformer such as a vari-ac V and the secondary of the variac is connected to the primary of a power transformer T which may be a 5000 volt, 300 volt-ampere power transformer or a 20 milliampere neon sign lighting transformer as above described. When employing the 5000 volt, 300 watt power transformer a resistance R which may have a value of about '70 ohms is placed in the primary lead of the transformer and an A. C. ammeter A of approximately two amperes range in the other. A capacitor C of about .001 to .008 microfarad is connected across the secondary leads of the transformer. This produces across the diamond a condensed spark discharge of very short duration and thus limits heating of the diamond. The rheostat R can be dispensed with if a current limiting transformer such as a 12,000 volt, 20 milliampere neon sign lighting transformer is used instead of the power transformer.

Control and speed of drilling is improved by inserting a quenched spark gap G in the secondary lead between the transformer T and the capacitor C. This prevents the formation of a power are follow-up in the circuit that would overheat and spoil the diamond. When this is done, however, the apparatus must be enclosed in a metallic shield S to avoid radio interference.

As shown in Fig. 3b, the drill stand for dry drilling of the pilot hole provides a metallic support for the diamond and an aligning support for the drilling needle together with electrical connections 8, 9, for connecting these two elements across the condenser 0, Fig. 3a. In the simple form of stand shown in Fig. 31) for purposes of illustration, two 3-inch brass angle pieces l0, II are fastened to a wooden pillar [2 which is supported by the base l3. A small brass rod [4 weighing approximately 5 to grams, slides closely but with minimum friction through two aligned guide holes drilled in the brass angle pieces. Into the lower end of the rod I4 is fastened the drilling needle l5 which for the purpose of step (2) in Fig. 1 is preferably a 70% platinum, 30% iridium wire approximately .020 inch in diameter. A brass block I6 provided with an upstanding brass table I! supports the diamond die blank 18.

With the arrangement shown in Figs. 3a and 3b it is not necessary to secure the unmounted diamond D to the pedestal I! at all, but if desired, we contemplate effecting such securement in any suitable way, for example, by the use of a drop of cellulose acetate cement, such as that currently sold under the trade-name Duco cement, between the diamond and the top of the pedestal H to prevent shifting of the diamond relative to the electrode 18, particularly during the initial spotting operation.

In this operation the end of the drill needle i5 is ground to a cone of about 20 degrees, and the point is brought into contact with the center of the flat surface of the die blank I8. The current is then applied and adjusted by means of the variac V until a white spark extends from the needle l5 to the brass pillar II. This should occur when the ammeter A reads about 1 ampere. The drilling proceeds rapidly with the diamond supported in the air or other gaseous atmosphere, and is a dry drilling procedure effected without wetting of the stone or immersion of it in any electrolyte. If the end of the drill !5 becomes red the current should be reduced by adjusting the variac V until the color disappears. The current should, however, be sufiicient to maintain the white spark between the drill I5 and the pillar H. In about 20 minutes time a roughly cylindrical hole, Fig. 1, step (2), about 0.5 mm. (0.020 inch) deep and .2 mm. (0.008 inch) in diameter, is drilled in the diamond and the end of the drill I5 is disintegrated. Very little progress is made at this point by repeating the dry drilling operation with a resharpened needle.

(3) Countersinking According to our present invention, the foredrilled blank I8 is next mounted on the light drilling machine employing a suitable blunt or wide-angled countersink, for example, a No. 1 drill needle, sharpened to a 90 cone and rotated at a relatively high speed, for example, 3200 R. P. M. Using grade 45 micron powder in alcohol or any other suitable vehicle, and reciprocating the diamond axially of the needle at a slow rate, say 200 times per minute, so that the powder may enter between the needle point and. diamond surface, the bell cone is then countersunk to the bottom of the foredrilling as indicated in Fig. 1, step (3), in about 45 minutes. During this operation the die is applied against the countersinking point about of the time with a very light pressure, of the order of a few which the drill needle 20 is carried by a vertical shaft 21 rotated in a bearing 22 by any suitable means as the cord and pulley drive 23. The diamond I8 is mounted on a support 24, which is shown as provided with a height adjusting means 25, andcarried by an arm 26 pivoted at 21 and adapted to raise and lower the support 24 as aforesaid. In the form shown a lightly loaded counterweight 28 lifts the diamond against the drill point, and the arm reciprocating cam 29, suitably driven, effects the displacement of the blank I8 from contact with the drill point.

The countersinking proceeds so rapidly by the method described that a convenient means of quick examination is essential to efficient performance of the countersinking operation, and for this purpose, the blank 18 is mounted in a newly developed small window-nib illustrated in Fig. 4. This nib, in the form shown, comprises a cylindrical cup shaped member 30 provided with two diametrically aligned viewing openings 31 and with a close fitting cylindrical plug 32 having a conical reservoir 33 to hold the dustand-vehicle mixture. The reservoir 33, as shown, narrows to an axial center opening, and the diamond blank is sealed to the plug 32 by a thin layer of wax on the bottom of the plug in the space 34 surrounding this center opening. This layer of wax prevents leakage of the cutting mix and also enables the blank [8 to be lifted from the cup 30 by lifting out the plug 32, which may be provided with a flange around its upper end to facilitate its removal, if desired. Beeswax, dental wax, or the like, makes a good seal from which the diamond is easily disengaged. The window on the diamond, when it is secured in the nib, is aligned with the openings 3|, so that the progress of the drilling may be seen through one of these openings, the blank being illuminated by light shining through the other. With this unit the blank l8 can be mounted or unmounted in a few moments.

(4) Pilot extension In the next step, Fig. 1, step (4), by repeating the dry drilling operation of step (2) (see Figs. 3a-3b) the foredrilling is extended an additional 0.5 mm. (0.020 inch) in about 20 minutes.

(5) Finishing the bell Following the pilot extension the blank is again returned to the drilling machine, and further countersunk with a needle ground to a 60 cone, as shown in Fig. 1, step (5). Using grade 20 micron powder at the start and grade 6 micron powder to finish, a smooth 60 cone about 1.0 mm. (.040 inch) deep is obtained in about an hour. The set-up is generally like that employed in step (3) (see Fig. 4). At this point about 0.2 mm. (.008 inch) of the blank thickness should be left for the secondary cone. If the finished blank is to be more than 1.2 mm. thick, say 1.6 mm., further foredrilling and countersinking of the bell may be practiced.

(6) Further treatment After formation of the bell in accordance with the present invention, the secondary cone of the die may be formed in any suitable manner, and the die may then be completed by back-opening and blending and polishing as desired. Preferably these operations are performed in accordance with the method disclosed in the above mentioned copending application, but such further procedure forms no part of the present invention.

(7) Economies In forming a bell cone employing the present invention, the foredrilling and countersinking, repeated until the desired depth of bell is obtained, may be effected in about 3 hours per die. One operator can care for two electric drills or ten countersinking spindles, and thus the time required for forming a bell by the present invention becomes approximately 40 to 60 man minutes per die.

By contrast, in the prior art bruting and pecking method an average of 2.5 man hours is required per bell, and inaddition considerable consumption of diamond chips and powder is involved in the bruting and pecking operations.

The present invention contributes greatly to the noteworthy saving of material, labor, and time, effected by the process as a whole in the producing of a better and more uniform bell which in its initial production is generated with a well polished surface. These and other advantages may be more fully appreciated from a consideration of the aforesaid copending application and publication, to which reference is made in this connection.

From the foregoing description of a preferred method and. apparatus illustrative of the invention, it will be appreciated that the invention is not limited to the precise embodiment disclosed, but includes modifications thereof, as will be apparent from the appended claims.

What is claimed is:

1. In the production of small diamond dies and the like, the method which comprises forming the die blank with two parallel polished faces and a polished window face perpendicular thereto, extending a pilot hole part way into the blank, mounting the blank in a holder exposing said polished window face to view and providing for illumination of said blank from behind, and enlarging the diameter of the pilot hole to shape it to a wide angled cone by rotary drilling with a vertical axis blunt needle point and diamond dust under relative reciprocation of the blunt needle and holder to'countersink said pilot hole to substantially its full depth without apexial contact of the drill needle with the diamond, while observing the progress of the countersinking through said exposed window face.

2. The method of mounting for countersinking, a diamond die blank formed with two parallel faces and with a polished window face perpendicular thereto and having a pilot well extending part-way into the diamond substantially perpendicularly to one of said parallel faces, which consists in adhesively securing said diamond to a perforated plug with its pilot well aligned with the perforation thereof, inserting said diamond supporting plug diamondend first into a substantially vertically open'cup against the bottom of which the other parallel face of said diamond rests, and which has aligned viewing openings adjacent said bottom, orienting said plug to orient the window face of said diamond with one of said viewing openings, and illuminating the diamond through the other of said viewing openings.

3. In apparatus for the production of small diamond dies and the like, a window nib comprising a cylindrical cup, said cup having a substantially fiat die blank supporting area in its bottom, said cup being provided with viewing apertures aligned for viewing of a die blank supported on said supporting area, a cylindrical plug slidably and removably fitting within said cup, said plug having an axial recess therein narrowing to a central opening in its bottom and having a substantially flat annular area surrounding said central opening and carrying adhesive means for sealing a die blank to said annular area, said plug, when inserted in said cup with a die blank adhesively secured to its under side, positioning said die blank on said supporting area so that it may be viewed through said viewing openings, and when then removed from said cup, carrying the die blank with it.

4. In apparatus for the production of small diamond dies and the like, a window nib comprising a cup-like member having a substantially flat die blank supporting area in its bottom, said cup-like member being provided with viewing apertures aligned for viewing of a die blank supported on said supporting area, a plug slidably and removably fitting within said cup-like member, said plug having a central recess therein narrowing to a central opening in its bottom and having a substantially flat facial area surrounding said central opening for carrying adhesive means for sealing a, die blank to said facial area, said plug, when inserted in said cup with a die blank adhesively secured to its under side, positioning said die blank on said supporting area so that it may be viewed through said viewing openings, and when then removed from said cup, carrying the die blank with it.

CHAUNCEY G. PETERS, FOREST K. HARRIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date H 1,885,178 Bsteh Nov. 1, 1932 2,374,942 Kurtz May 1, 1945 2,398,250 Robbins Apr. 9, 1946 2,402,411 Moses June 25, 1946 FOREIGN PATENTS Number Country Date 580,411 Great Britain Sept. 6, 1946 

